The chemistry of vanadium

Question 1

the oxidation number, formula, name and colour in aqueous solution of the 4 vanadium ions are:

Answer 1

• vanadium(II) , V2+ (aq) , +2 , purple
• vanadium(III), V3+ (aq) , +3, green
• oxovanadium(IV), VO 2+ (aq), 4+, blue
• dioxovanadium(V), VO2 + (aq), +5, yellow

Question 2

the usual source of vanadium with oxidation number +5 is the compound:

Answer 2

ammonium vanadate(V), NH4VO3

Question 3

an acidic solution of the NH4VO3 compound contains

Answer 3

the dioxovanadium ion, VO2 +

Question 4

when zinc is added to acidic solution of the NH4VO3 compound, the following redox reaction occurs:

Answer 4

the reduction of the VO2 + ion begins, with the gradual colour change from yellow, to blue, then green and finally purple as the oxidation number decerases from +5 to +2

(note that all these colours are solutions, there are no precipitates involved)